In the heavy industry, large and heavy products can be difficult to handle manually. Thus, a hoist connecting to a clamping device can be used to lift and move heavy objects. A object can be clamped to a clamping device that is coupled to a hoist. The hoist can lift the object to a certain height, and then transfer to a proper location.
The clamping devices can utilize a mechanism that converts the weight of the object into a clamping force, thus the holding force on the object exerted by the clamping devices can be proportional to the weight of the object. A loading and unloading device, such as a crane or a hoist, can be coupled to the clamping device for lifting and transferring the objects.
A basic prior art clamping device can include a rotatable clamping jaw, which can rotate to change a spacing distance to a fixed clamping jaw. Rotation of the rotatable clamping jaw can enlarge or narrow the distance between the two clamp jaws. For example, an object can be placed between the two jaws from a bottom position, and the pushed upward toward the gap between the two jaws. The upward motion of the object can cause a clockwise rotation of the rotatable clamping jaw, which can make the distance between the two jaws larger, to accommodate an object. After the object is placed between the two jaws, the weight of the object can cause the object to move downward. The downward motion of the object can cause a counterclockwise rotation of the rotatable clamping jaw, which can narrow the distance between the two jaws, or to exert a clamping force on the object.
FIG. 1A illustrates a prior art rotatable clamping device according to some embodiments. A clamping device 100 can include a clamp body 110, which can house a fixed clamp jaw 130 and a rotatable clamp jaw 120. The fixed clamp jaw and the rotatable clamp jaw can be configured to clamp an object 160. The rotatable clamp jaw can have an offset center of rotation 150, thus when the rotatable clamp jaw rotates counter clockwise, it comes closer to the fixed clamp jaw 130. That way the clamping device can support a number of sizes of objects. A spring 140 can preload the rotatable clamp jaw, e.g., to push the rotatable clamp jaw toward the fixed clamp jaw.
In operation, when the clamping device 100 is empty, e.g., when there is no object in the clamping device, the spring 140 pushes the rotatable clamp jaw counterclockwise toward the fixed clamp jaw, so there is no gap between the two jaws. An object 160 can be pushed in the clamping device, for example, upward to the space between the two jaws from a bottom position. The pushing action can open the gap between the two jaws by rotating the rotatable clamp jaw clockwise.
Gravity then hold the object in place, e.g., when the object is pulling out of the clamping device, for example, in a downward direction, the rotatable clamp jaw is rotated counterclockwise due to friction between the object and the contact surface of the rotatable clamp jaw. The rotation exerts a force on the object, preventing the object from being pulled out of the clamping device.
The rotatable clamping device can be compact and simple. But there can be focused force at the rotatable clamp jaw, e.g., at the contact area of the rotatable clamp jaw with the object. Thus the rotatable clamping device is not designed to handle heavy object, since heavy object requires a large clamping force, and the focused large clamping force might cause damage to the object.
Another prior art clamping device can include a gripping device normally fabricated from structural steel components, that are designed to securely hold and lift construction materials though a scissor movement. The gripping device can use freely rotating pin connections to create a scissor configuration with two scissor arms.
A first end of the scissor arms is configured to rotate towards each other in reaction to the opposite second end of the scissor arms being lifted vertically. The first end of the scissor arms rotate inwards and generate a compression force clamping on the object to be lifted. Essentially, the weight of the object is used to generate this clamping action.
FIG. 1B illustrates a prior art gripping device according to some embodiments.
A gripping device 105 can include two scissor arms 125 and 155, which can freely rotate about a pivot point 135. The scissor arms 125 and 155 can include upper arms 121 and 151, together with lower arms 122 and 152, respectively, connected through the freely rotating pivot 135.
The upper arms 121 and 151 can be coupled to pulling elements 141 and 142, respectively. The coupling between the upper arms and the pulling elements can include freely rotating pin connections, e.g., the pulling element 141/142 can be rotated relative to the upper arm 121/151. The pulling elements 141 and 142 can be coupled to a lift 145, such as a hoist. The coupling between the pulling elements and the lift can include freely rotating pin connections, e.g., the pulling elements 141 and 142 can be rotated relative to the lift 145.
The lower arms 122 and 152 can be coupled to holding pads 111 and 112, respectively. The coupling between the lower arms and the holding pads can include freely rotating pin connections, e.g., the holding pads 111/112 can be rotated relative to the lower arm 122/152.
In operation, an object 165 is placed between the holding pads 111 and 112. The lift 145 is pulled up, which pulls on the pulling elements 141 and 142. The pulling elements 141 and 142 can in turn pull on the upper arms 121 and 151. The scissor movement between the upper arms 121/151 and the lower arms 122/152 around the pivot point 135 can turn the pulling action on the upper arm 121/151 into a pressing action of the lower arm 122/152, which presses on the object 165 through the holding pads 111 and 112.
Disadvantages of the gripper devices can include large sizes due to the long arms. For example, if the friction coefficient between the holding pads and the object is about 0.2, then a five times the weight of the object is needed to hold the object. In other words, the ratio of the upper arms and the lower arms is also about five to obtain the holding force.